如何仿寫簡易tomcat 實現思路+代碼詳細講解

仿寫之前，我們要搞清楚都要用到哪些技術

自定義注解，比如Tomcat使用的是@Servlet，我們可以定義一個自己的@MyServlet
構造請求體和返回體，比如tomcat使用HttpRequest，我們可以自己定義myHttpRequest
java去遍歷一個指定目錄，然后獲取到.java文件，再獲取到帶有@MyServlet注解的類
然后將這個注解里的path和這個類本身映射成map
通過反射去調用該類的方法（doGet、doPost）
還需要用到socket來監聽消息，并且對監聽到的消息進行處理

第一步：自定義注解

@Target(ElementType.TYPE)
@Documented
@Retention(RetentionPolicy.RUNTIME)
public @interface MyServlet {String path() default "";
}

第二步：定義HttpRequest以及HttpResponse、

public class MyHttpRequest {//定義一個map，用來存放請求體中的參數，key是參數名稱，value是參數值public Map<String,String> map = new HashMap<>();public String getParameter(String key){return map.get(key);}
}

public class MyHttpResponse {public OutputStream outputStream;public static final String responsebody = "HTTP/1.1 200+\r\n" + "Content-Type：text/html+\r\n"+ "\r\n";public MyHttpResponse(OutputStream outputStream) {this.outputStream = outputStream;}
}

第三步：遍歷整個目錄，把Java文件放入list中

    private static void func(File file){File[] files = file.listFiles();String s;for (File file1 : files) {if (file1.isDirectory()){func(file1);}if (file1.isFile()){//取src之后的名字s = file1.toString().split("src")[1];//去掉src后邊的第一個\，得到全類名s = s.substring(1);//判斷是不是以.java結尾的文件if (s.length() >=5 && s.substring(s.length() - 5).equals(".java")){//把全類名中的\替換成.s = s.replace('\\','.');//去掉后綴名.javas = s.substring(0,s.length()-5);//把類名加入到list中javaclasses.add(s);}}}}

第四步：找出帶有Servlet注解的Java文件，并把注解中的path，類對象放入到map中

    public static void getServlet() throws ClassNotFoundException {for (int i = 0; i < javaclasses.size(); i++) {String path = javaclasses.get(i);Class<?> cl = Class.forName(path);if (cl.isAnnotationPresent(MyServlet.class)){servletMap.put(cl.getAnnotation(MyServlet.class).path(),cl);}}}

第五步：創建socket連接

InetAddress localHost = InetAddress.getLocalHost();System.out.println("localhost" + localHost);ServerSocket serverSocket = new ServerSocket(8080, 10, localHost);System.out.println("等待建立連接");Socket server = serverSocket.accept();System.out.println("連接已建立");

第六步：定義線程接收報文

        HttpAcceptThread httpAcceptThread = new HttpAcceptThread(server);Thread accept = new Thread(httpAcceptThread);accept.start();accept.join();

HttpAcceptThread類內容如下：

class HttpAcceptThread implements Runnable{private Socket socket;ArrayList<String> strings = new ArrayList<>();public HttpAcceptThread(Socket socket) {this.socket = socket;}@Overridepublic void run() {System.out.println("開始接收http");try {BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));String s;while ((s = reader.readLine()).length() != 0){try {strings.add(s);System.out.println(s);} catch (Exception e){System.out.println("接收Http進程結束");break;}}System.out.println("接收http進程結束");} catch (IOException e) {e.printStackTrace();}}
}

第七步：處理httprequest，也就是通過反射去調用doGet和doPost方法

這一步有些復雜，尤其是對url切割時，但我給每一步都加了注釋，方便理解

? ? ? ? ? ? ?GET /address1?a=111&b=222

   private static void requestHttp(Socket socket,String http) throws IOException, NoSuchMethodException, InstantiationException, IllegalAccessException, InvocationTargetException {//GET /address1?a=111&b=222（拿獲取到的這個url舉例）//先通過空格判斷是GET還是POSTString requestStyle = http.split(" ")[0];if (requestStyle.equals("GET")){//如果是GET，取空格后面部分，即/address1?a=111&b=222String httpPathAndParameter = http.split(" ")[1];//定義httpPathString httpPath;//創建httpRequest對象MyHttpRequest myHttpRequest = new MyHttpRequest();//通過索引位置判斷url里邊有沒有帶？if (httpPathAndParameter.indexOf("?") != -1){//如果有，由于有個/,因此我們要先拿到address1?a=111&b=222這部分httpPath = httpPathAndParameter.substring(1);//獲取問號前面部分，即address1，\\作為轉義字符使用httpPath = httpPath.split("\\?")[0];System.out.println(httpPath);//獲取問號后面部分的所有參數String parameterString = httpPathAndParameter.split("\\?")[1];//使用&分開String[] parameters = parameterString.split("&");for (int i = 0; i < parameters.length; i++) {//把參數及其值仿佛request的map中myHttpRequest.map.put(parameters[i].split("=")[0],parameters[i].split("=")[1]);}} else {//如果不存在？，也就說明不存在參數，我們只需要獲取httpPathhttpPath = httpPathAndParameter.substring(1);System.out.println(httpPath);}//創建HttpResponse對象OutputStream outputStream = socket.getOutputStream();MyHttpResponse myHttpResponse = new MyHttpResponse(outputStream);//反射調用doGetClass servletClass = servletMap.get(httpPath);Method doGet = servletClass.getMethod("doGet", MyHttpRequest.class, MyHttpResponse.class);doGet.invoke(servletClass.newInstance(),myHttpRequest,myHttpResponse);} else {//如果不是Get請求，也按照同樣的步驟，先取出/address1String httpPath = http.split(" ")[1];//去掉/,只留下address1httpPath = httpPath.substring(1);System.out.println(httpPath);MyHttpRequest myHttpRequest = new MyHttpRequest();OutputStream outputStream = socket.getOutputStream();MyHttpResponse myHttpResponse = new MyHttpResponse(outputStream);//根據httpPath取出類信息Class servletClass = servletMap.get(httpPath);//獲取doPost方法Method doPost = servletClass.getMethod("doPost", MyHttpRequest.class, MyHttpResponse.class);//調用doPost方法doPost.invoke(servletClass.newInstance(),myHttpRequest,myHttpResponse);}}

最后一步：把上面這些方法整合起來，在主方法中調用，同時定義好全局變量

public class MyTomcat {//用于存放Java類的全類名public static ArrayList<String> javaclasses = new ArrayList<>();//用于存放Servlet的類對象，其中key是Servlet的url，value是servlet的類對象public static HashMap<String,Class> servletMap = new HashMap<>();public static void main(String[] args) throws ClassNotFoundException, IOException, InterruptedException, InvocationTargetException, NoSuchMethodException, InstantiationException, IllegalAccessException {String inputPath = "D:\\JavaProject\\practice\\src\\tomcat";File file = new File(inputPath);//獲取.java后綴文件，并獲取全類名func(file);System.out.println(javaclasses);//獲取帶有servlet注解的類對象，并放到map中。getServlet();System.out.println(servletMap);InetAddress localHost = InetAddress.getLocalHost();System.out.println("localhost" + localHost);ServerSocket serverSocket = new ServerSocket(8080, 10, localHost);System.out.println("等待建立連接");Socket server = serverSocket.accept();System.out.println("連接已建立");//定義線程接收http報文HttpAcceptThread httpAcceptThread = new HttpAcceptThread(server);Thread accept = new Thread(httpAcceptThread);accept.start();accept.join();//處理請求requestHttp(server,httpAcceptThread.strings.get(0));}

然后就可以進行測試了，在測試類上方加上我們已經定義好的@MyServlet注解

@MyServlet(path = "address1")
public class Servlet1 {public void doGet(MyHttpRequest request, MyHttpResponse response) throws IOException {System.out.println("address1 GET響應：");System.out.println("a=" + request.getParameter("a"));System.out.println("\n響應的http如下：");String resp = MyHttpResponse.responsebody + "<!DOCTYPE html>\n" +"<html>\n" +"<head>\n" +"    <meta charset=\"utf-8\" />\n" +"</head>\n" +"<body>\n" +" \n" +"    <form name=\"my_form\" method=\"POST\">\n" +"        <input type=\"button\" value=\"按下\" onclick=\"alert('你按下了按鈕')\">\n" +"    </form>\n" +" \n" +"</body>\n" +"</html>";System.out.println(resp);response.outputStream.write(resp.getBytes());response.outputStream.flush();response.outputStream.close();}public void doPost(MyHttpRequest request, MyHttpResponse response) throws IOException {System.out.println("\n響應的http如下：");String resp = MyHttpResponse.responsebody +"{\"sorry\":\"we only respond to method GET now\"},\r\n" +"";System.out.println(resp);response.outputStream.write(resp.getBytes());response.outputStream.flush();response.outputStream.close();}
}

然后啟動項目